Recently, each of the membrane shells used in the membrane separation apparatus is independent, and is at least provided with one raw water port and one concentrated water port. During the engineering installation, when the raw water port and one concentrated water port of each of the membrane shells are respectively assembled with the raw water port and one concentrated water port of other membrane shells or a pipeline, each of the joints requires a clamp for connection, thus requiring a large number of clamps, which causes high construction cost. In addition, in the prior art, there are multiple sealed points, the hidden seepage danger is high, the workload for the engineering installation is great, and the occupied area of the apparatus is large. Therefore, there is an urge need to solve the above problems.